Today, I’m going to review my online test, chapter 3 of Oracle Certified Associate (OCA), provided by SYBEX. If you need to access to this online resources, you need to buy their book first. See https://sybextestbanks.wiley.com/.

Question 4

What is the result of the following code?

StringBuilder sb = new StringBuilder();
sb.append("aaa").insert(1, "bb").insert(4, "ccc");
System.out.println(sb);

1. abbaaccc
2. abbaccca
3. bbaaaccc
4. bbaaccca
5. An exception is thrown.
6. The code does not compile.

The answer is B. At the beginning, the string is empty. Then, threes characters had been appended into the char array, so the array contained three a characters. After that, two b had been added into the char array at index 1, and the remaining characters were shifted. Same idea for adding ccc.

['a', 'a', 'a']
['a', 'b', 'b', 'a', 'a']
['a', 'b', 'b', 'a', 'c', 'c', 'c', 'a']

Question 14

Which of the following can replace the comment to print "avaJ"? (Choose all that apply)

StringBuilder puzzle = new StringBuilder("Java");
// INSERT CODE HERE
System.out.println(puzzle);

1. puzzle.reverse();
2. puzzle.append("vaJ$").substring(0, 4);
3. puzzle.append("vaJ$").delete(0, 3).deleteCharAt(puzzle.length - 1);
4. puzzle.append("vaJ$").delete(0, 3).deleteCharAt(puzzle.length);
5. None of the above.

The answer is AC. In this example, the choice A is correct because the method reverse reverses the characters sequence stored inside the string builder. The answer B is wrong because of 2 points: the returned substring is wrong, and StringBuilder#substring returns a string but not a string builder, so even if the result is right, it must be retrieved immediately from return statement. Answer C is correct since JavavaJ$ can be transformed into avaJ by removing the first three characters and the last character.

Question 27

What is the result of the following?

List<String> one = new ArrayList<String>();
one.add("abc");
List<String> two = new ArrayList<>();
two.add("abc");
if (one == two)
  System.out.println("A");
else if (one.equals(two))
  System.out.println("B");
else
  System.out.println("C");

1. A
2. B
3. C
4. An exception is thrown.
5. The code does not compile.

The answer is B. Because list one and list two are equal by value, but they are not equal by reference.

Question 31

What is the output of the following code?

LocalDate date = LocalDate.of(2018, Month.APRIL, 30);
date.plusDays(2);
date.plusYears(3);
System.out.println(date.getYear()
    + " " + date.getMonth()
    + " " + date.getDateOfMonth());

1. 2018 APRIL 2
2. 2018 APRIL 30
3. 2018 MAY 2
4. 2021 APRIL 2
5. 2021 APRIL 30
6. 2021 MAY 2
7. A runtime exception is thrown.

The answer is B. Local date is an immutable object, so any modification of such object creates a new date object. Since there’s no code retrieving the returned value, the returned value is ignored. Therefore, option B is correct.

Question 32

What is the output of the following code?

LocalDateTime d = LocalDateTime.of(2015, 5, 10, 11, 22, 33);
Period p = Period.of(1, 2, 3);
d = d.minus(p);
DateTimeFormatter f = DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT);
System.out.println(d.format(f));

1. 3/7/14 11:22 AM
2. 5/10/15 11:22 AM
3. 3/7/14
4. 5/10/15
5. 11:22 AM
6. The code does not compile.
7. A runtime exception is thrown.

The answer is E. Even though d has both date and time. the formatter only outputs time.

Question 33

What is the output of the following code?

LocalDateTime d = LocalDateTime.of(2015, 5, 10, 11, 22, 33);
Period p = Period.ofDays(1).ofYears(2);
d = d.minus(p);
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
System.out.println(d.format(f));

1. 5/9/13 11:22 AM
2. 5/10/13 11:22 AM
3. 5/9/14
4. 5/10/14
5. 11:22 AM
6. The code does not compile.
7. A runtime exception is thrown.

The answer is B. Period does not allow chaining. Only the last Period method called counts, so only the two years are subtracted.

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